Tri-cone bits for horizontal and hard formation drilling applications

ABSTRACT

The present invention discloses a tri-cone drill bit comprising: three head sections with upper parts thereof jointed together to form a bit body, three cones rotatably mounted to lower ends of the head sections respectively, nozzle sockets designed on the bit body between respective head sections and each having a hole in which a nozzle is mounted, wherein gage cutters are mounted to an upper trailing side of each head O.D. surface to form a gage holding surface thereon, and a leading side of each head section is backwardly slanted as a whole. The design of gage surface at trailing sides of head sections increases the bit&#39;s stability, reduces lateral vibration and also reduces tendency of bit deflection in horizontal drilling applications and effective working life of the bit is improved. Backward slant of leading sides of head sections facilitates upward carrying of drilling cuttings and improves drilling efficiency. Jets from the nozzles are respectively directed to the leading side of each following cone, which enhances bottom hole cleaning and cooling of cutting elements and leads to a longer working life and higher ROP of the bit.

CROSS-REFERENCE TO RELATED APPLICATION

The instant nonprovisional patent application claims priority to Chinese Patent Application No. 200810048635.3, filed Jul. 30, 2008, and which is incorporated by reference in its entirety herein for all purposes.

BACKGROUND OF THE INVENTION Technical Field

The present invention is related to roller cone drill bits, particularly to tri-cone bits used for horizontal and hard formation drilling applications associated with subterranean drilling and oil and gas drilling applications.

Existing tri-cone bit normally comprises a bit body provided with three head sections. Three cones are mounted respectively on each bearing shaft at lower ends of head sections which are tilted downwardly and inwardly, and the cones are machined with steel cutters or mounted with WC (tungsten carbide) inserts. Drilling fluid flows from a drill string into the bit's watercourse and then is jetted out from three nozzles mounted in nozzle sockets that are located at trailing sides of respective head sections. After impinging the bottom hole, the drilling fluid then flows up from the sides of nozzle sockets via an annular space between the bit and the borehole wall. Three points on heel row cutters of each cone contact the borehole wall and such contacting points are located at the leading side of each cone. When drilling horizontal wells and hard formations, such drill bits have the following problems: fast lateral movement and strong impact would result in offset of a rotational center of the bit from its geometric center, thereby accelerating wear and breakage of cutting elements and even causing premature failure of bit bearings. Moreover, insufficient cuttings removal from the bottom hole because of the gravity would also cause wear on cone shell, breakage or loss of cutting elements. Unreasonable orientation of drilling fluid jets would result in untimely cooling of cutting elements, thereby accelerating wear on the cutting elements. In order to cope with lateral vibration, wear resistant inserts were arranged at an upper part of head O.D. (Outside Diameter) by some prior arts. However, centers of such wear resistant inserts on head P.D. are normally on an axis of the head section, which is not sufficient to restrain severe lateral vibrations.

One method described in U.S. Pat. No. 6,227,314 entitled as ‘INCLINED LEG EARTH-BORING BIT’ is to change the nozzle socket position from rear to front side, a lower portion of each bit leg is inclined backwards and offset circumferentially from the upper portion thereof. Accordingly, a gage portion is formed at the upper part of the leg O.D., and a drilling fluid return passage is formed on an exterior surface of the bit body between each of the nozzle socket and at least one of the bit legs, but this passage changes direction at upper part of the leg and is not beneficial to the up-flowing of the drilling fluid.

In another method described in U.S. Pat. No. 6,688,410 entitled as ‘HYDRO-LIFTER ROCK BIT WITH PDC INSERTS’, none of rolling cone cutters extends to gage diameter of the bit. Instead, a plurality of cutting elements are mounted on a backface of each leg, and said plurality of cutting elements have at least one cutting element with a cutting tip that extends to the gage diameter. A geometric centerline of an upper part of the leg is in parallel with a centerline of the bit, and an angle is formed between a geometric centerline of a lower part of the leg and the centerline of the bit. With this invention, the borehole diameter is formed by leg O.D. and drilling efficiency of the bit might be limited.

BRIEF SUMMARY OF THE INVENTION

This invention is intended to provide a tri-cone bit especially for horizontal and hard formation drilling applications in order to solve existing technical problems mentioned above. The bit of this invention can effectively mitigate lateral vibrations of a roller cone bit when drilling horizontal wells and hard formations. It has a better bottom hole cleaning effect to further improve drilling efficiency of the bit.

In accordance with teachings of the present disclosure, there is provided a tri-cone drill bit for horizontal and hard formation drilling applications comprising: three head sections with upper parts thereof jointed together to form a bit body, three cones rotatably mounted to lower ends of respective head sections, nozzle sockets designed on the bit body between respective head sections and each having a hole in which a nozzle is mounted, wherein gage cutters are mounted to an upper trailing side of each head O.D. surface to form a gage surface thereon, and a leading side of each head section is backwardly slanted as a whole.

In one embodiment, said backward slant of the leading side of each head section is in the range of 10° to 50° , and normally, this range is from 10° to 30°.

In one embodiment, a jet from said nozzle in each nozzle socket is directed to the leading side of a respective rotationally following cone.

In one embodiment, a portion of the upper trailing side of each head O.D. surface where the gage cutters are mounted has a diameter less than the gage diameter by 0 to 2 mm. The said gage cutters are tungsten carbide inserts or diamond enhanced WC inserts.

Technical benefits of the present invention include: (1) the design of gage holding surface at trailing side of head sections increases the bit's stability, reduces lateral vibration and also reduces tendency of bit deflection in horizontal drilling applications and therefore effective working life of the bit is improved; (2) backward slant of leading side of head sections forms unrestricted drilling fluid up-flow channel and also creates raising force to drilling cuttings and thus facilitates upward carrying of drilling cuttings and improves drilling efficiency; (3) jets from the nozzles are respectively directed to leading side of each following cone and this will lead the drilling fluid directly spurt at and clean the cutting elements of the cones at working, which enhances bottom hole cleaning and cooling of cutting elements and leading to longer working life and higher ROP of the bit.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete and better understanding of the present invention and advantages thereof may be achieved by referring to the following descriptions taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:

FIG. 1 is a front view of an embodiment of the present invention;

FIG. 2 is a bottom view of an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiment and its advantages can be best understood with reference to FIGS. 1-2 in which like numbers refer to the same or like parts.

The present invention has disclosed an improved tri-cone bit comprising three head sections 3 and respective cones 4 rotatably mounted onto lower ends of the head sections. Upper parts of the three head sections are jointed together by welding to form a bit body. Tapered threads 1 are machined on an upper portion or shank of the bit body for connection with a drill string. Gage cutters are arranged at an upper part of the head O.D. surface near a trailing side of each head section. Alternatively, each head O.D. surface might have an upper trailing side extending backwardly by a certain distance where gage cutters are arranged. Two or three rows of gage cutters, with 2 to 3 gage cutters in each row, are mounted on the head O.D. surface. The gage cutters in adjacent rows might be arranged in a staggered fashion. The gage cutters might be tungsten carbide inserts or diamond enhanced WC inserts, and form a gage surface on upper parts of head sections. A portion of the upper gage surfaces of head sections where the gage cutters are mounted has a diameter less than the gage diameter of the bit by 1 mm. With such a gage surface at upper parts of the head sections, three centralizing points are added along a circumference of the bit. Thus, take the original three points in heel row cutters of the bit that contact the borehole wall into consideration, totally six points of centralization is achieved. Compared with the conventional case of three points centralization, lateral stability of the bit is greatly enhanced.

A leading side of each head section 2 is backwardly slanted by a slanted angle, i.e. the included angle with a vertical line, is 20° to 30° to thus form a drilling fluid up-flowing channel which could apply a relatively high raising force to drilling cuttings and thus facilitate upward carrying of drilling cuttings. Nozzle sockets 8 are designed on the bit body between respective head sections and close to trailing sides of respective head sections. The bit body is provided with a watercourse that is in fluid communication with each nozzle socket, especially with a jet hole of the nozzle socket in which a nozzle 7 is mounted. A jet 6 from each nozzles 7 is directed toward the leading side of each rotationally following cone, and a minimum distance from a jet potential core to cutting elements of the rotationally following cone is zero, so that an effective cooling of the cutting elements 5 can be achieved when entering a working plane and during drilling. 

1. A tri-cone drill bit for horizontal and hard formation drilling applications comprising: three head sections with upper parts thereof jointed together to form a bit body, three cones rotatably mounted to lower ends of respective head sections, nozzle sockets designed on the bit body between respective head sections and each having a hole in which a nozzle is mounted, wherein gage cutters are mounted to an upper trailing side of each head O.D. surface to form a gage surface thereon, and a leading side of each head section is backwardly slanted as a whole.
 2. The drill bit as defined in claim 1 wherein said backward slant of the leading side of each head section is in the range of 10° to 50°.
 3. The drill bit as defined in claim 2 wherein said backward slant of the leading side of each head section is in the range of 10° to 30°.
 4. The drill bit as defined in claim 1 wherein a jet from said nozzle in each nozzle socket is directed to the leading side of a respective rotationally following cone.
 5. The drill bit as defined in claim 2 wherein a jet from said nozzle in each nozzle socket is directed to the leading side of a respective rotationally following cone.
 6. The drill bit as defined in claim 4 wherein a jet potential core of the jet from the nozzle has a minimum distance of zero from cutting elements of the rotationally following cone.
 7. The drill bit as defined in claim 5 wherein a jet potential core of the jet from the nozzle has a minimum distance of zero from cutting elements of the rotationally following cone.
 8. The drill bit as defined in claim 1 wherein a portion of the upper trailing side of each head O.D. surface where the gage cutters are mounted has a diameter less than the gage diameter by 0 to 2 mm.
 9. The drill bit as defined in claim 2 wherein a portion of the upper trailing side of each head O.D. surface where the gage cutters are mounted has a diameter less than the gage diameter by 0 to 2 mm.
 10. The drill bit as defined in claim 1 wherein said gage cutters are tungsten carbide inserts or diamond enhanced WC inserts.
 11. The drill bit as defined in claim 2 wherein said gage cutters are tungsten carbide inserts or diamond enhanced WC inserts.
 12. The drill bit as defined in claim 1 wherein each head O.D. surface have the upper trailing side extended backwardly by a certain distance where gage cutters are arranged.
 13. The drill bit as defined in claim 1 wherein two or three rows of said gage cutters, with 2 to 3 gage cutters in each row, are mounted to head O.D. surfaces in a staggered manner.
 14. The drill bit as defined in claim 12 wherein two or three rows of said gage cutters, with 2 to 3 gage cutters in each row, are mounted to head O.D. surfaces in a staggered fashion. 